A motor used in a hybrid electric vehicle outputs high power and has a high space factor of coil for reduction in motor size. This may cause a problem in a temperature rise of the motor coil in use. Accordingly, a demand has been increased for a method of cooling the coil at a high cooling efficiency. When the temperature of the coil rises, a limiter for upper limit temperature is activated for system safety. Consequently, there may occur problems of deterioration in steep-hill climbing capability (gradeability), high-load steady running, and others.
JP2004-215358A discloses a technique of directly cooling by air flow an annular bus bar exposed on a coil with a heat conductive insulating member interposed therebetween.